The sensitivity of many optical and electro optical devices to the polarization of the incoming light pulses poses a serious problem in many optical systems including optical communications systems and optical computing systems. Although light pulses in such systems may be generated with a known polarization, as the light pulses propagate through the system the polarization may be changed by polarization drift which may in turn depend on the temperature and strains in the propagation medium, among other factors. Additionally, if a receiver in such a system is receiving light pulses generated by multiple sources in the system, not all sources will generate light pulses having the same initial polarization and as a result, even if there is no polarization drift, the receiver will not be receiving light pulses of one polarization from all the sources. By the term pulse it is meant a packet of optical energy of finite extent.
Previous attempts at developing polarization independent devices have been only partially successful because such devices tend to either be limited in bandwidth or are energy inefficient. For example one method of reducing polarization sensitivity is to preprocess the incoming signal so as to produce signals of a known predetermined polarization. One such device for accomplishing this utilizes an electro-optical polarization analyzer in conjunction with a polarization changing device. The polarization analyzer measures the polarization of the incoming light pulse and tunes the polarization state changing device to produce light pulses of the required polarization. The measurement and tuning required for such a system introduces both latency and bandwith limitations which may be unacceptable at high data rates.
Another device for reducing polarization sensitivity uses a polarizing beamsplitter to split the light pulse into two orthogonal linearly polarized components. One of the linear components is then rotated 90.degree. so as to be aligned and then recombined with the other linear component with a time delay sufficient to avoid interference. Although this produces a closely spaced pair of output pulses of a known linear polarization, about half of the energy in the initial pulse is lost in the conversion process.
The present invention avoids the shortcomings of the prior art.